Printed Circuit Board Having Flow Preventing Dam And Manufacturing Method Thereof

ABSTRACT

Disclosed is a printed circuit board having a flow preventing dam and a manufacturing method thereof The printed circuit board includes a base substrate having a solder pad, a solder bump formed on the solder pad of the base substrate, and a flow preventing dam formed on a peripheral area of the base substrate using a dry film resist. The flow preventing dam can prevent the outflow of an underfill solution and can be simply formed.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2008-0112362, filed Nov. 12, 2008, entitled “A printed circuit boardhaving a flow preventing dam and a manufacturing method of the same”,which is hereby incorporated by reference in its entirety into thisapplication.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printed circuit board (PCB) having aflow preventing dam and a manufacturing method thereof, and moreparticularly to a PCB having a flow preventing dam, in which the flowpreventing dam is provided on the peripheral area of the PCB so as toprevent the outflow of an underfill solution which is introduced betweenthe PCB and a semiconductor chip which is flip chip bonded thereto.

2. Description of the Related Art

With the recent advancement of electronics industries, there is a demandfor increasing performance and functionality of electronic componentsand reducing the size thereof. Accordingly, high integration, slimnessand fine circuit patterning are also required on a substrate for surfacemounting components, such as SIP (System in Package), 3D package, etc.

In particular, in techniques for mounting electronic components on thesurface of a substrate, a wire bonding process or a flip chip bondingprocess is utilized for electrical connection between an electroniccomponent and a substrate.

The wire bonding process includes bonding an electronic component havingdesign circuits to a PCB using an adhesive, connecting a lead frame ofthe PCB to a metal terminal (i.e., pad) of the electronic componentusing a metal wire to transmit and receive information therebetween, andmolding the electronic component and the wire with thermosetting resinor thermoplastic resin.

The flip chip bonding process includes forming an external connectionterminal (i.e., bump) having a size of tens of μm to hundreds of μm onan electronic component using a material such as gold, solder or anothermetal, and flipping the electronic component having the bump so that thesurface thereof faces the substrate and is thus mounted on thesubstrate, unlike the mounting operation based on the wire bonding.

Although the wire bonding process has higher productivity compared toother packaging processes, it needs wires for connection to the PCB, andthus the size of a module is increased and an additional procedure isrequired. Hence, the flip chip bonding process is mainly employed.

FIGS. 1 and 2 are views showing a process of packaging a flip chipsemiconductor package according to a conventional technique.

As shown in FIGS. 1 and 2, the flip chip bonding according to theconventional technique is performed in a manner such that solder balls16 are attached to the connection pads 14 of a PCB 12 and asemiconductor chip 18 is mounted on the PCB 12 by means of the solderballs 16.

In this way, however, when the semiconductor chip 18 is mounted on thePCB 12, a gap G is formed between the semiconductor chip 18 and the PCB12 due to the height of the solder balls 16 attached to the connectionpads 14 of the PCB 12, undesirably weakening the ability to support thesemiconductor chip 18 and causing cracks around the soldering portion ofthe solder balls 16. In particular, in the case where a temperaturechange occurs, the coefficient of thermal expansion between thesemiconductor chip 18 and the PCB 12 is different, and thus thermalstress is applied to the solder balls 16, thereby causing cracks on thesolder balls 16.

Hence, with the goal of stably supporting the semiconductor chip 18, anunderfill solution 22 of a liquid material is introduced into the gap Gbetween the semiconductor chip 18 and the PCB 12 using a dispenser 20.

The underfill solution 22 is introduced in a small amount between thesemiconductor chip 18 and the PCB 12 and thus functions as an adhesivefor holding the chip and plays a role in protecting the chip from theexternal environment, unlike a conventional semiconductor moldingmaterial (EMC) for packaging the entire semiconductor chip 18.

However, in the course of introducing the underfill solution 22 usingthe dispenser 20, part of the underfill solution 22 which is introducedinto the gap G between the semiconductor chip 18 and the PCB 12 mayundesirably overflow the outer edge of the PCB 12 from the positionwhere the dispenser 20 is located, causing defects.

In order to solve this problem, there have been proposed methods offorming a dam on the peripheral area of the PCB using a dispensingprocess.

However, the dispensing process which is used to form a linear damthrough linear extrusion of epoxy resin from a dispensing nozzle isproblematic in that the width of the dam may be non-uniform, and theshape of the dam may become winding due to frictional force at the endof the dispensing nozzle.

Further, an additional dispensing apparatus is required to form the dam,and a process for forming the dam should be additionally carried out.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind theproblems encountered in the related art and the present inventionprovides a PCB having a flow preventing dam, which is able to preventthe outflow of an underfill solution, and a manufacturing methodthereof.

In addition, the present invention provides a PCB having a flowpreventing dam, in which the flow preventing dam is formed using a dryfilm resist for forming a solder bump without a need for an additionaldispensing apparatus or dispensing process, and a manufacturing methodthereof.

According to a preferred embodiment of the present invention, a PCBhaving a flow preventing dam includes a base substrate having a solderpad, a solder bump formed on the solder pad of the base substrate, and aflow preventing dam formed on the peripheral area of the base substrateusing a dry film resist.

As such, a solder resist layer having an opening for exposing the solderpad may be formed on the base substrate.

The flow preventing dam may include the dry film resist which isattached in a state of being overcured through excessive exposure to thesolder resist layer.

Also, a semiconductor chip which is flip chip bonded to the basesubstrate by means of the solder bump formed on the solder pad of thebase substrate may be further included.

The flow preventing dam may be provided to protrude from the basesubstrate along the outer edge of the semiconductor chip, in order toprevent the outflow of an underfill solution which is introduced into agap between the semiconductor chip and the base substrate.

The flow preventing dam may be formed to be lower than the upper surfaceof the semiconductor chip which is flip chip bonded to the basesubstrate and to be higher than the gap between the semiconductor chipand the base substrate.

The flow preventing dam may be provided between the outer edge of thebase substrate and the outer edge of the semiconductor chip.

In addition, according to another preferred embodiment of the presentinvention, a method of manufacturing a PCB having a flow preventing damincludes (A) applying a dry film resist on a base substrate having asolder pad, and then primarily exposing the dry film resist to light,(B) secondarily exposing the primarily exposed dry film resist formed ona peripheral area of the base substrate to light, thus forming a flowpreventing dam, (C) removing the unexposed dry film resist to expose thesolder pad, thus forming an opening, (D) printing the opening with asolder paste and then forming a solder bump through a reflow process,and (E) removing the primarily exposed dry film resist.

After (E) removing the primarily exposed dry film resist, (F) flip chipbonding a semiconductor chip to the base substrate by means of thesolder bump formed on the solder pad of the base substrate may befarther included.

After (F) flip chip bonding the semiconductor chip, (G) introducing anunderfill solution into a gap between the semiconductor chip and thebase substrate may be further included.

The flow preventing dam may be provided to protrude from the basesubstrate along the outer edge of the semiconductor chip, in order toprevent outflow of an underfill solution which is introduced into thegap between the semiconductor chip and the base substrate.

The flow preventing dam may be formed to be lower than an upper surfaceof the semiconductor chip which is flip chip bonded to the basesubstrate and to be higher than the gap between the semiconductor chipand the base substrate.

The flow preventing dam may be provided between the outer edge of thebase substrate and the outer edge of the semiconductor chip.

Also, a solder resist layer having an opening for exposing the solderpad may be formed on the base substrate.

The features and advantages of the present invention will be moreclearly understood from the following detailed description taken inconjunction with the accompanying drawings.

Further, the terms and words used in the present specification andclaims should not be interpreted as being limited to typical meanings ordictionary definitions, but should be interpreted as having meanings andconcepts relevant to the technical scope of the present invention basedon the rule according to which an inventor can appropriately define theconcept implied by the term to best describe the method he or she knowsfor carrying out the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are views showing a process of packaging a flip chipsemiconductor package according to a conventional technique;

FIG. 3 is a cross-sectional view showing a PCB having a flow preventingdam according to a preferred embodiment of the present invention;

FIG. 4 is a cross-sectional view showing the PCB having a flowpreventing dam according to the preferred embodiment of the presentinvention, to which a semiconductor chip is flip chip bonded;

FIG. 5 is a top plan view of FIG. 4; and

FIGS. 6 to 13 are cross-sectional views showing the process ofmanufacturing the PCB having a flow preventing dam according to thepreferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The features and advantages of the present invention will be moreclearly understood from the following detailed description and preferredembodiments taken in conjunction with the accompanying drawings. In thedescription, the terms “first”, “second” and so on do not indicate anyparticular amount, sequence or importance but are used only todistinguish one element from another element. Throughout the drawings,the same reference numerals refer to the same or similar elements, andredundant descriptions are omitted. In order to make the characteristicsof the invention clear and for the convenience of description, adetailed description pertaining to the other known techniques may beomitted.

Hereinafter, a detailed description will be given of the preferredembodiment of the present invention, with reference to the accompanyingdrawings.

PCB having Flow Preventing Dam

FIG. 3 is a cross-sectional view showing the PCB having a flowpreventing dam according to the preferred embodiment of the presentinvention. With reference to this drawing, the PCB 100 having a flowpreventing dam according to the preferred embodiment of the presentinvention is described below.

As seen in FIG. 3, the PCB 100 having a flow preventing dam according tothe present invention includes a base substrate 102 having solder pads104, solder bumps 116 formed on the solder pads 104, and a flowpreventing dam 110 c formed on a peripheral area thereof.

The base substrate 102 is configured such that the solder pads 104 areformed on either or both surfaces thereof and a solder resist layer 106having openings for exposing the solder pads 104 is formed.

The flow preventing dam 110 c is composed of a dry film resist which isattached in a state of being overcured through excessive exposure to thesolder resist layer 106.

FIGS. 4 to 5 are a cross-sectional view and a top plan view showing thePCB having a flow preventing dam according to the preferred embodimentof the present invention, to which a semiconductor chip is flip chipbonded;

As shown in FIGS. 4 and 5, the semiconductor chip 118 is flip chipbonded to the base substrate 102 by means of the solder bumps 116 formedon the solder pads 104 of the base substrate 102, and an underfillsolution 120 is introduced between the semiconductor chip 118 and thebase substrate 102.

The flow preventing dam 110 c is provided to protrude from the basesubstrate 102 along the outer edge of the semiconductor chip 118, thuspreventing the outflow of the underfill solution 120.

The flow preventing dam 110 c is provided between the outer edge of thebase substrate 102 and the outer edge of the semiconductor chip 118, andis formed to be higher than the gap G between the base substrate 102 andthe semiconductor chip 118 and to be lower than the upper surface of thesemiconductor chip 118, in order to prevent the outflow of the underfillsolution 120.

Method of Manufacturing PCB having Flow Preventing Dam

FIGS. 6 to 13 are cross-sectional views showing the process ofmanufacturing the PCB having a flow preventing dam according to thepreferred embodiment of the present invention.

With reference to FIGS. 6 to 13, the method of manufacturing the PCBhaving a flow preventing dam according to the present invention isdescribed below.

As shown in FIG. 6, a dry film resist 110 is applied on the basersubstrate 102 having solder pads 104.

The base substrate 102 is configured such that the solder pads 104 areformed on one surface thereof and the solder resist layer 106 havingopenings 108 for exposing the solder pads 104 is formed on the basesubstrate 102.

The dry film resist 110 includes a photoresist in a film form, a mylarfilm formed on one surface of the photoresist to impart flexibilitythereto, and a cover film formed on the other surface thereof.

The dry film resist 110 is applied in a state of peeling off the coverfilm using a typical dry film laminating apparatus.

The dry film resist 110 may be formed to a predetermined thickness inconsideration of the size of the solder bumps 116 and the height of theflow preventing dam 110 c.

Next, as shown in FIG. 7, the portion of the dry film resist 110, otherthan the portion of the dry film resist 110 applied on the solder pads104, is subjected to a primary exposure process.

The primary exposure process is performed by exposing the portion of thedry film resist 110, other than the portion thereof applied on thesolder pads 104, to UV light, using a mask (not shown) having apredetermined pattern.

The primarily exposed dry film resist 110 b, other than the unexposeddry film resist 110 a applied on the solder pads 104, is cured throughpolymerization in the primary exposure process.

Next, as shown in FIG. 8, the primarily exposed dry film resist 110 aformed on the peripheral area of the base substrate 102 is subjected toa secondary exposure process, thus forming the flow preventing dam 110c.

As such, the secondarily exposed dry film resist, which forms the flowpreventing dam 110 c, is overcured through excessive exposure and isthus more firmly attached to the solder resist layer 106. Accordingly,the dam is not removed in a subsequent dry film resist strippingprocess.

Next, as shown in FIG. 9, the unexposed dry film resist 110 a is removedthrough a development process to expose the solder pads 104, thusforming openings 112.

The development process is performed by dissolving and removing theuncured portion other than the cured portion due to UV exposure, andthus the unexposed dry film resist 110 a is removed using a developersuch as sodium carbonate (Na₂CO₃) or potassium carbonate (K₂CO₃).

Next, as shown in FIG. 10, the openings 112 are printed with a solderpaste.

The solder paste 114 is printed through a screen printing in a mannersuch that the base substrate 102 is disposed on a printing table, a maskhaving a plurality of openings is placed on the base substrate, and thesolder paste is pressed into the openings of the mask using a squeegee.

Next, as shown in FIG. 11, the printed solder paste 114 is subjected toa reflow process, thus forming solder bumps 116.

The solder paste 114 printed in the openings 112 of the dry film resist110 is formed in a round shape through a reflow process to be lower thanthe flow preventing dam 110 c. In the case where the semiconductor chip118 is mounted on the solder bumps 116, the gap G between the basesubstrate 102 and the semiconductor chip 118 is lower than the flowpreventing dam 110 c, and therefore the flow preventing dam 110 c canprevent the outflow of the underfill solution which is introduced intothe gap G.

As shown in FIG. 12, the primarily exposed dry film resist 110 b isremoved.

The primarily exposed dry film resist 110 b may be stripped using astripping solution such as NaOH or KOH.

In the course of bonding the OH— of the stripping solution with thecarboxyl group (COOH+) of the dry film resist, the primarily exposed dryfilm resist 110 b gets loose and thus is stripped. Because thesecondarily exposed dry film resist, namely, the flow preventing dam 110c, is attached in a state of being overcured through excessive exposureto the solder resist layer 106, it is not removed by the strippingsolution.

As shown in FIG. 13, the semiconductor chip 118 is flip chip mounted onthe base substrate 102 by means of the solder bumps 116, and theunderfill solution 120 is introduced into the gap G between the basesubstrate 102 and the semiconductor chip 118, thus completing a flipchip package.

The flow preventing dam 110 c is provided to protrude from the basesubstrate along the outer edge of the semiconductor chip 118, and isformed to be higher than the gap between the base substrate 102 and thesemiconductor chip 118 and to be lower than the upper surface of thesemiconductor chip 118, thereby preventing the outflow of the underfillsolution.

As described hereinbefore, the present invention provides a PCB having aflow preventing dam and a manufacturing method thereof. According to thepresent invention, the flow preventing dam is provided, thus preventingthe expansion and outflow of an underfill solution.

Also, according to the present invention, the flow preventing dam isformed through excessive exposure of a dry film resist used in thecourse of forming solder bumps, thus obviating a need for additionalmaterial, apparatus, and process.

Also, according to the present invention, the flow preventing dam can beformed with the dry film resist, and thus the height and width thereofare uniform.

Also, according to the present invention, the outflow of the underfillsolution is prevented, thus improving the overall package reliability.

Although the preferred embodiment of the present invention regarding thePCB having a flow preventing dam and the manufacturing method thereofhas been disclosed for illustrative purposes, those skilled in the artwill appreciate that various modifications, additions and substitutionsare possible within the scope of the invention.

1. A printed circuit board having a flow preventing dam, comprising: abase substrate having a solder pad; a solder bump formed on the solderpad of the base substrate; and a flow preventing dam formed on aperipheral area of the base substrate using a dry film resist.
 2. Theprinted circuit board as set forth in claim 1, wherein a solder resistlayer having an opening for exposing the solder pad is formed on thebase substrate.
 3. The printed circuit board as set forth in claim 1,wherein the flow preventing dam comprises the dry film resist which isattached in a state of being overcured through excessive exposure to thesolder resist layer.
 4. The printed circuit board as set forth in claim1, further comprising a semiconductor chip which is flip chip bonded tothe base substrate by means of the solder bump formed on the solder padof the base substrate.
 5. The printed circuit board as set forth inclaim 4, wherein the flow preventing dam is provided to protrude fromthe base substrate along an outer edge of the semiconductor chip, inorder to prevent outflow of an underfill solution which is introducedinto a gap between the semiconductor chip and the base substrate.
 6. Theprinted circuit board as set forth in claim 4, wherein the flowpreventing dam is formed to be lower than an upper surface of thesemiconductor chip which is flip chip bonded to the base substrate andto be higher than the gap between the semiconductor chip and the basesubstrate.
 7. The printed circuit board as set forth in claim 4, whereinthe flow preventing dam is provided between the outer edge of the basesubstrate and the outer edge of the semiconductor chip.
 8. A method ofmanufacturing a printed circuit board having a flow preventing dam,comprising: applying a dry film resist on a base substrate having asolder pad, and then primarily exposing the dry film resist to light;secondarily exposing the primarily exposed dry film resist formed on aperipheral area of the base substrate to light, thus forming a flowpreventing dam; removing the unexposed dry film resist to expose thesolder pad, thus forming an opening; printing the opening with a solderpaste, and then forming a solder bump through a reflow process; andremoving the primarily exposed dry film resist.
 9. The method as setforth in claim 8, further comprising flip chip bonding a semiconductorchip to the base substrate by means of the solder bump formed on thesolder pad of the base substrate, after removing the primarily exposeddry film resist.
 10. The method as set forth in claim 9, furthercomprising introducing an underfill solution into a gap between thesemiconductor chip and the base substrate, after flip chip bonding thesemiconductor chip.
 11. The method as set forth in claim 9, wherein theflow preventing dam is provided to protrude from the base substratealong an outer edge of the semiconductor chip, in order to preventoutflow of an underfill solution which is introduced into the gapbetween the semiconductor chip and the base substrate.
 12. The method asset forth in claim 9, wherein the flow preventing dam is formed to belower than an upper surface of the semiconductor chip which is flip chipbonded to the base substrate and to be higher than the gap between thesemiconductor chip and the base substrate.
 13. The method as set forthin claim 9, wherein the flow preventing dam is provided between theouter edge of the base substrate and the outer edge of the semiconductorchip.
 14. The method as set forth in claim 8, wherein a solder resistlayer having an opening for exposing the solder pad is formed on thebase substrate.